HealthDay News -- Being lonely does more than just make a person feel sad -- loneliness can affect a person's physical health, researchers report.

In a study of 200 breast cancer survivors, average age 51, compared to study participants with more social connections, people who said they felt lonely showed more inflammation in response to stress, and higher levels of reactivation of a latent herpes virus, which is a sign of poor immunity.

The investigators also noted that the reactivation of a latent herpes virus is known to be linked with stress, and said these findings suggest that loneliness acts as a chronic source of stress that triggers a poorly controlled immune response.

The study was scheduled for presentation Saturday at the annual meeting of the Society for Personality and Social Psychology in New Orleans. The data and conclusions of research presented at medical meetings should be viewed as preliminary until published in a peer-reviewed journal.

"It is clear from previous research that poor-quality relationships are linked to a number of health problems, including premature mortality [death] and all sorts of other very serious health conditions. And people who are lonely clearly feel like they are in poor-quality relationships," study author Lisa Jaremka, a postdoctoral fellow at the Institute for Behavioral Medicine Research at Ohio State University, said in a university news release.

"One reason this type of research is important is to understand how loneliness and relationships broadly affect health," she explained. "The more we understand about the process, the more potential there is to counter those negative effects -- to perhaps intervene. If we don't know the physiological processes, what are we going to do to change them?"